Hydroxyl group phenolic

Ion-exchange resins. The constituent phenolic hydroxyl groups in the insoluble phenol-formaldehyde resins react with cations of salts ... 

The phenolic hydroxyl group of tyrosine, the imidazole moiety of histidine, and the amide groups of asparagine and glutamine are often not protected in peptide synthesis, since it is usually unnecessary. The protection of the hydroxyl group in serine and threonine (O-acetylation or O-benzylation) is not needed in the azide condensation procedure but may become important when other activation methods are used. 

The best known aryl ester is O acetylsalicylic acid better known as aspirin It is pre pared by acetylation of the phenolic hydroxyl group of salicylic acid... 

Chemical Properties. Lignin is subject to oxidation, reduction, discoloration, hydrolysis, and other chemical and enzymatic reactions. Many ate briefly described elsewhere (51). Key to these reactions is the ability of the phenolic hydroxyl groups of lignin to participate in the formation of reactive intermediates, eg, phenoxy radical (4), quinonemethide (5), and phenoxy anion (6) ... 

The effect substitution on the phenolic ring has on activity has been the subject of several studies (11—13). Hindering the phenolic hydroxyl group with at least one bulky alkyl group ia the ortho position appears necessary for high antioxidant activity. Neatly all commercial antioxidants are hindered ia this manner. Steric hindrance decreases the ability of a phenoxyl radical to abstract a hydrogen atom from the substrate and thus produces an alkyl radical (14) capable of initiating oxidation (eq. 18). 

Codeine, like morphine, is isolated from the opium poppy. However, the low yield of 0.7—2.5% does not provide sufficient material to meet commercial demands. The majority of marketed codeine is prepared by methylating the phenolic hydroxyl group of morphine. Morphine yields from opium poppy are 4—21%. When prescribed for cough, the usual oral dose is 10—20 mg, three to four times daily. At these doses, adverse side effects are very few. Although the abuse potential for codeine is relatively low, the compound can substitute for morphine in addicts (47). 

Above 160°C it is believed that additional cross-linking reactions take place involving the formation and reaction of quinone methides by condensation of the ether linkages with the phenolic hydroxyl groups (Figure 23.14). 

Polymer systems are now available which may be cured by reaction of epoxy resin compounds with the phenolic hydroxyl groups. Such reactions do not evolve volatile by-products. These materials are showing promise in the area of heat-resisting electrical insulation laminates. 

EtOH), is insoluble in benzene or ether, and sparingly in chloroform, but dissolves readily in alkali, the solution darkening in air. The salts are crystalline but unstable. The base forms a crystalline metbiodide and contains two methoxyl and two phenolic hydroxyl groups. On methyla-tion it yields a mixture of corydine and fsocorydine. On exhaustive methylation corytuberine yields eventually trimethylamine and 3 4 5 6-tetramethoxy-8-vinylphenanthrene, m.p. 69°. 

Processes for the extraction of the total alkaloids and isolation of the-individual bases will be found in the papers cited above. Cephaeline is too toxic for medical use and is usually converted into emetine by methyla-tion of the phenolic hydroxyl group, and processes have been patented for this purpose, beginning with that of Wellcome, Carr and Pyman in 1913. ... 

Huonnations with DAST proceed with high chemoselectivity In general, under very mild reaction conditions usually required for the replacement of hydroxyl groups, other functional groups, including phenolic hydroxyl groups [112], remain intact This provides a method for selective conversion of hydroxy esters [95 97] (Table 6), hydroxy ketones [120, 121], hydroxy lactones [722, 123], hydroxy lactams [124] and hydroxy nitriles [725] into fluoro esters, fluoro ketones, fluoro lactones, fluoro lactams, and fluoro nitnles, respectively (equations 60-63)... 

Incorporation of a phenolic hydroxyl group greatly attenu-... 

It was projected that compound 13 could be stereoselectively linked, through its free phenolic hydroxyl group, with the anomeric carbon of intermediate 12 under suitably acidic conditions (see Scheme 8). Gratifyingly, the action of boron trifluoride etherate on a mixture of 12 and 13 in CH2CI2 at -50 °C induces a completely stereoselective glycosidation reaction, providing the desired a-ano-mer 48 in an excellent yield of 95 % from 46. It is presumed that boron trifluoride initiates cleavage of the anomeric trichloroacetimi-... 

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